1. Field of the Invention
This invention relates to communication networks. More specifically, the invention relates to Local Area Networks (LANs) of the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) type which provide both half-duplex and full-duplex communication channels.
2. Description of the Prior Art
Ethernet is a commonly used name for a network access protocol of the CSMA/CD type. The CSMA/CD protocol is defined in ANSI/IEEE Standard 802.3, published by the Institute of Electrical and Electronic Engineers, Inc., 3445 East 45th Street, New York, N.Y. 10017, and referred to as the IEEE 802.3 standard. Under the CSMA/CD rules for access to a network, any node or station wishing to transmit must first "listen" to make sure that the channel is clear before beginning to transmit. All nodes on the network have equal priority of access and after a required inter-packet delay (IPG) of 9.6 .mu.s (microseconds) may begin transmitting as soon as the channel is clear. However, if the first node that has started transmitting detects a "collision" with a transmission from another node, the first node continues transmitting for a short time to make sure that all nodes wishing to transmit will detect the collision. Every other node detecting collision also continues to transmit for a short time. Then each node that has detected a collision terminates transmission of the packet or frame. The nodes involved in the collision enter a collision avoidance mode. In the collision avoidance mode, the nodes wait for the required IPG of 9.6 .mu.s and then use different delay times, referred to as backoff times, before trying transmission of the same packet again. When the number of nodes is small, e.g. two nodes, the IEEE standard 802.3 exhibits an undesirable effect, referred to as the "capture effect" in which one of the nodes may effectively capture and transmit a succession of data packets which essentially "freezes out" the other node from transmitting messages.
The nature of ethernet is changing in that there are now multiple methods of connecting to a network. Ethernet can be connected in half-duplex, half-duplex switched or full-duplex switched domains. Each of these environments has characteristics that define the highest performing method of transmitting data on the network. When the network hardware is programmed to operate half-duplex, which is the standard node for ethernet, chaining transmit packets together can result in poor network performance due to the speeds at which some signal drivers can drive the network, particularly when the network is in a high traffic collision domain. In a lightly loaded half-duplex network, however, there is less need to incur artificially extended inter-packet delay between packets or frames, since the level of competition for the network is greatly reduced. On the other hand, in full-duplex, it is not necessary to incur an artificially extended inter-packet delay since the station is no longer competing for access to the network. Therefore, in full-duplex it is more beneficial not to incur the overhead of artificially extended inter-packet delay between packets, since there is no competition for the network.
Accordingly, there is a need to provide an ethernet driver transmit technique for both half and full-duplex that maximizes performance of the network in terms of latency and throughput, regardless of whether half or full-duplex is being used on the network.
The prior art related to the problem addressed by the present invention is, as follows:
European patent application 063,262,082 entitled "Backoff Time Evaluation Method for ethernet," published Apr. 1, 1995, discloses an ethernet capture effect avoidance scheme which uses a special capture avoidance binary exponential backoff (CABEB) algorithm.
A publication entitled "Solving Capture in Switched Two-Node Ethernets By Changing Only One Node" by W. Hayes, et al. published in the proceedings, Twentieth Conference on Local Computer Networks, Minneapolis, Minn., USA, Oct. 16-19, 1995, pages 387-95, discloses a method for solving capture effect in switched multi-mode ethernet systems by allowing a node to keep a local copy of attempts counter of other nodes and to use this information to trigger switching its medium access protocol policy between two extremes, one aggressively persistent and the other completely passive.
U.S. Pat. No. 5,432,775 entitled "Auto Negotiation System for a Communication Network," issued Jul. 11, 1995, filed Dec. 3, 1993, discloses a system for detection of enhanced capability of stations on a communications network. A specified pattern of late test pulses are detected and transmitted to provide for the indication of enhanced capability. The system is particularly useful for determining whether a particular station is in full-duplex or half-duplex mode without affecting overall network performance.
U.S. Pat. No. 5,305,317 issued Apr. 19, 1994, discloses an adaptive circuit for a local area network whereby the adaptive circuit can operate in a token ring protocol or in an ethernet protocol. A protocol handler is operable to communicate with internal buses in either a token ring or ethernet protocol.
None of the prior art addresses the problem of dynamically tuning ethernet device drivers for improved network performance, i.e., latency and throughput, regardless of whether the network hardware is in a half or full-duplex mode, and without the use of special algorithms or other mechanisms to alter the inter-packet delay gap for collision avoidance.